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I converted from a manual to a TH-400 too. I couldn't easily find the factory kickdown parts when I did the swap, so I opted for this Lokar unit. So far, so good. http://www.lokar.com/product-pgs/throttlecables-kickdowns/tc-kd-pgs/th400kd.html
The kickdown on a TH400 is an electrical switch on the accelerator pedal.